In the winter of 2018, I worked on hardforking the Vertcoin network to a new version of its proof-of-work algorithm. Vertcoin is a cryptocurrency that aims to be profitably mineable by people on commodity hardware (GPUs). Since the previous version of the proof-of-work algorithm got dominated by specialized hardware, the development team decided to tweak the algorithm into a new version, and hardfork the network. The hardfork was completed succesfully at block 1080001.
On top of the Core client’s hardfork code, which is further detailed in this pull request, there was also work involving the upgrade of the Insight and P2Pool code.